This invention relates to the method and the device for controlling the temperature of all utensils for cooking on a burner element particularly on the surface burner element of a range. There are many types of ranges equipped with surface burner elements presently in use. Some surface burner elements of electric ranges are in the form of spiral sheathed heating elements, while others have a flat heat transfer top made of either glass, metal alloy, or ceramic with the heating elements located underneath such top. Others use natural gas for heating. The challenge is to create a regulating device which can provide safe control of the cooking temperature of the utensil placed on the heating element. Most electric ranges in use nowadays do not have any cooking temperature control per se; a device commonly referred to as a heat switch is used to regulate the current to the burner element so as to vary its heating power. The heat switch may be in the form of a mechanical switch provided with a current coil or a current control electronic circuit which operates to vary the heating power of the burner element. Malfunction of such current control would inevitably result in a run away operation of the burner element, namely the burner element would operate continuously with increasing power to result ultimately in a fire hazard. In cooking, it is, in fact, the temperature of the utensil that actually cooks the food contained within it. However, by controlling the heating power output of the burner element, the actual cooking temperature is unknown. Since utensils of various sizes and volumes may be used for cooking and also various types and volumes of food are being cooked, it is necessary to re-adjust the heat switch when using utensils of different sizes and volumes for cooking various types and amount of food. The user has to estimate the appropriate setting of the heating power of a burner element, depending on the size of the utensil, and the amount of food to be cooked in the utensil. The heat switch varies the current to the burner element with a series of ON and OFF cycles so as, in turn, to vary its heating power. Such method of merely varying the heating power does not provide a satisfactory cooking operation when using utensils of different shapes and sizes for cooking foods having various masses of liquids and/or solids so that the heat losses, as well as the thermal capacities may vary widely; therefore, the same amount of heat applied to two very different utensils will result in two very different actual cooking temperatures. Furthermore, the heat required to raise the temperature of the utensil is often much higher than the heat required to maintain the utensil at a desired cooking temperature. Most users would turn the heat switch control dial to the maximum heat setting in order to save time in heating the utensil to the desired cooking temperature quickly; and it is intended to turn the control dial down to a lower maintenance heat setting after the utensil has attained the desired temperature. However, often time, the user forgets to do so, resulting in dire consequences in which the cooking pot may become overheated, or even melted, or the cooking oil or similar flammable substance inside the pot may be ignited. Kitchens and whole houses have been known to burn down in many cases due to such negligence.
In U.S. Pat. No. 4,492,336 to Takata et al and U.S. Pat. No. 4,470,888 to Ceste et al, temperature controls for particular types of cooking vessels are shown. Such temperature controls do not cater to universal applications for cooking with different types of cooking utensils such as boiling water in a kettle, or heating a large stew pot; and they cannot be used for controlling common cooking utensils intended for use in cooking with different types of conventional surface burner elements.
There have been attempts to sense directly the temperature of the utensil during cooking by means of infrared devices, such as those shown in U.S. Pat. 4,734,553 to Noda and U.S. Pat. No. 4,499,357 to Kojima. However, these methods and devices suffer the critical drawback that the infrared waves can be blocked by the lid, handle, or other parts of the utensil to render them inoperative. Thus, there is a great demand that the temperature sensing method and device must be capable of sensing directly the actual cooking temperature of any cooking utensil which is heated on all types of conventional burner elements so that the application of the method and device is universal. Furthermore, the method and device must be capable of turning off the burner element when there is no cooking utensil placed thereon or to prevent the burner element from operating in a runaway condition.